There has been proposed an image forming apparatus of a type that includes an image bearing body having a surface on which an electrostatic latent image is formed, a toner cartridge containing toner for developing the electrostatic latent image, a developing member for subjecting the toner from the toner cartridge to frictional electrification and applying the toner to the surface of the image bearing body, thereby developing the electrostatic latent image into a toner image, a transfer member for transferring the toner image from the image bearing body to a recording medium, and a developing device which incorporates at least the developing member and in which the toner cartridge is removably provided. In the image forming apparatus of this type, after an electrostatic latent image is formed on the surface of the image bearing body, the developing member applies the toner from the toner cartridge to the surface of the electrostatic latent image bearing body by frictional electrification, thus developing the latent image. A toner image is thereby formed. Then, the transfer member transfers the toner image to a recording medium. As a result, an image corresponding to the electrostatic latent image is formed on the recording medium. Since the toner cartridge can be removed from the developing device that incorporates the developing member, the toner cartridge can be replaced by a new one when the toner is consumed up. Thus, image formation can be continued.
U.S. Pat. No. 5,867,756 has proposed an image forming apparatus of this type, in which a supplying member, such as an agitator, is provided in the toner cartridge to supply toner from the toner cartridge to the developing device and a returning member, such as auger rollers, is provided in the housing of the developing device, to return the toner from the developing device into the toner cartridge. The supplying member and the returning member are operated at the same time, thereby circulating toner between the developing device and the toner cartridge. Thus, the toner is prevented from coagulating and hardening at a particular position. Fluidity is ensured for the toner, enhancing the quality of images.